Transmission – Design

Design and Function

Applies to: 2007–011A; M56

Clutch, general

The main task of a clutch system is to transfer torque, disengage during shifting, allow comfortable starting and to act as an efficient vibration damper to eliminate noise and vibration in the chassis and drive train.

The clutch is between the engine and transmission. It consists mainly of a pressure plate and a clutch driven plate. The clutch transfers torque to and from the transmission and then on to drive the wheels.

The clutch is a single disc dry clutch. The clutch disc is connected to the transmission input shaft on the transmission.

Clutch driven plate

The clutch driven plate is the section that transfers the torque to the input shaft and into the transmission. It also plays a major role in ensuring gentle and comfortable starting.

The clutch driven plate has no damper and friction element. Instead these functions are integrated into the dual mass flywheel.

The clutch driven plate center is greased internally when the clutch driven plate is installed at the factory. This reduces the friction between the clutch driven plate and the input shaft to make shifting easier.

When replacing the clutch driven plate, the input shaft must be lubricated. See the instructions for replacing the clutch.

Concentric slave cylinder (CSC)

The clutch control mechanism is fully hydraulic. The slave cylinder is inside the clutch cover. There is no mechanical transfer (fork) inside the clutch cover from an external slave cylinder.

The concentric slave cylinder (CSC) means that the slave cylinder is integrated with the throwout bearing.

The concentric slave cylinder (CSC) is extremely efficient and reliable and the throwout bearing is accurately centered.

The unit is secured to the transmission cover using two screws. The bearings and friction surfaces do not need to be lubricated. The bearing on the concentric slave cylinder (CSC) is self-centering against the clutch diaphragm spring.

The hydraulic line from the master cylinder is connected to the concentric slave cylinder (CSC) via an adapter. There is a bleed nipple on the adapter.

There are ratios built-in to the system to reduce the force required to transfer torque:

• pedal effort
• hydraulic force
• clutch finger force.

The force is reduced from approximately 7800 N at the clutch to approximately 80 N at the pedal.

If the clutch pedal returns too quickly, the drive train could be damaged by the high torque. There is a shock load limiter in the clutch to avoid this. The shock load limiter chokes the flow between the concentric slave cylinder (CSC) and the master cylinder if there is a danger of the excessive torque. The shock load limiter is in the angle adapter, under the bleed nipple.

The concentric slave cylinder (CSC) is approximately 8 mm shorter for M66 than M56.

Dual mass flywheel

The dual mass flywheel reduces noise from the transmission and improves drivability.

The dual mass flywheel also helps reduce the load on the crankshaft bearings. It also improves shift quality because the flywheel mass on the clutch driven plate is lower.

The component parts of the dual mass flywheel can turn in relation to each other. The amount by which they turn depends on the engine load. On a dual mass flywheel the component parts can turn by up to 60 degrees in both directions. A certain amount of turning can be felt between the component parts if a dual mass flywheel is turned.

Transmission, general

M56 is a five gear manual transmission. The transmission and final drive are integrated in the same housing. The pressed aluminum housing halves are called the transmission housing and the clutch cover.

The movements of the gear selector lever are transferred to the transmission via two heavy duty mechanical cables. This reduces the effort required when shifting and gives a distinct feel for each gear position. All gears are synchronized. The oil is synthetic so the transmission does not require oil changes.

In the transmission there are three short parallel shafts on which the gear wheels are mounted. There is also a differential with a ring wheel. The bearings for the shafts and differential in the housing sections are conical roller bearings. All idler wheels have needle bearings. Both output shafts are constantly engaged in the final drive.

There are four selector rods in the transmission. There are gear selector forks on three of these selector rods. These three can move axially in the transmission.

The gear shift selector on the control lever assembly which is turned by the selector sleeve, transfers the shift motion directly or indirectly via a flange or a lever. Each synchronizing hub is joined to its shaft by splines and rotates with it.

The fourth selector rod is joined to the lateral movement lever. These are connected to the gear selector lever by mechanical cables.

Transmission, internal components

• A: Primary shaft
• B: Lower output (secondary) shaft
• C: Upper output (secondary) shaft.

The gear wheels are on three short and parallel shafts. These are the input shaft and two output (secondary) shafts which are both constantly engaged in the gear on the final drive. This means only two meshings for each forward gear. Despite having three shafts, this gives the same efficiency as two shaft transmissions.

The design using three short shafts gives the shafts rigidity which minimizes the risk of bending under high loads and consequent incorrect meshing.

All gears, including back-up (reverse), are synchronized. This means that back-up (reverse) gear can be selected without uncomfortable scraping noises from the gear wheels, even if the gear wheels in the transmission are not completely still on engagement.

The gear wheels, idler wheels and synchronizing units are on each shaft as follows:

• Primary shaftconsists of an input shaft with the gears for 1st and 2nd as well as the gears for 5th, the idler wheel for 4th gear, the synchronizing unit for 3rd and 4th and the idler wheel for 3rd gear
• Lower output (secondary) shaftconsists of an output shaft for gears 1, 2, 3, 4, the gear wheel for final drive, the idler wheel for 1st gear (also operates as the intermediate gear for back-up (reverse) gear), the synchronizing unit for 1st-2nd, the idler wheel for 2nd gear, and the gear wheels for 3rd and 4th
• Upper output (secondary) shaftconsists of an output shaft for gear 5 and back-up (reverse), gear wheel for the final drive for back-up gear, the idler wheel for back-up gear, the synchronizing unit for back-up and 5th gear and the idler wheel for 5th gear.

The teeth are treated after hardening so that they work as quietly as possible. By the use of tall, narrow teeth and optimized engagement angles a high number of teeth can engage. Back-up (reverse) gear also has helical teeth and operates as quietly as the other gears.

The ring wheel and gear wheel for final drive are on the differential housing. The differential housing includes the differential gears (with and without driveshaft splines) and a planetary shaft with lock.

Gear selector

The transmission has four selector rods. There are gear selector forks on three of these selector rods. The shift motion is transferred by double mechanical cables from the gear selector lever to the transmission. The selector pin on the differential gear allows for longitudinal shift movements. The gear selector and gearshift gate are on the input gear selector rod which is connected to the lever for lateral movement. The back-up (reverse) inhibitor prevents back-up (reverse) gear from being accidentally selected when shifting from 5th to 4th gear.

The mechanical transmission cable for lateral travel is adjustable. The mechanical transmission cable for longitudinal travel is not adjustable. If there is a fault or damage in/to one of the mechanical cables, both must be replaced at the same time.

The inner gear selector control in the transmission is in sliding bearings which are lubricated by the transmission fluid.

Back-up (reverse) inhibitor

There is a spring-loaded back-up (reverse) inhibitor connected to the gearshift gate which prevents the gear selector lever from moving to back-up (reverse) gear from 5th gear. The back-up (reverse) inhibitor normally rests on a lug on the gearshift gate.

Differential

The differential distributes power equally between the drive wheels, even if they are rotating at different speeds.

The differential consists of the differential housing, large and small differential gears, shaft journals and a thrust washer.

Synchronization

The synchronizing units are positioned on the shafts in the transmission as follows:

• The synchronizing unit for 1st - 2nd gear is on the lower output (secondary) shaft (output shaft for gears 1, 2, 3, 4)
• The synchronizing unit for 3rd - 4th gear is on the primary shaft
• The synchronizing unit for 5th/back-up (reverse) gear is on the upper output (secondary) shaft (output shaft for 5th and back-up (reverse) gear).

The synchronizing hub assembly consists of a coupling sleeve, flange and the hub. Each synchronizing hub is joined to its shaft by splines and rotates with it.

There are idler wheels on both sides of each synchronizing hub. The idler wheels rotate freely on the shaft. Each idler wheel is constantly engaged in its gear.

The synchronizing rings expand when heated by the same amount as the components they are in contact with. As a result no safety margin is required to counter expansion.

The idler wheels for single and double synchronization have no cones. An inner ring on the synchronizer unit performs this function instead.

The synchronizer unit is a modular system. This makes it easy to upgrade from a single synchronizer to double synchronization by replacing the synchronizer kit.

Single synchronization, which has one friction surface, is on:

• back-up (reverse) gear
• 4th gear
• 5th gear.

The outer ring (to the left in the illustration) is manufactured in pressed steel. The inner ring is pressed steel and the friction surface is coated with sintered brass.

Double synchronization, two friction surfaces, is on:

• 3rd gear.

The outer ring (to the left in the illustration) is manufactured in pressed steel. The sealing ring is pressed steel and the friction surfaces are coated with sintered brass. The inner ring is machined steel.

Triple synchronization, three friction surfaces, is on:

• 1st gear
• 2nd gear.

The outer ring (to the left in the illustration) is manufactured in pressed steel. The sealing ring is pressed steel and the friction surfaces are coated with sintered brass. The inner ring is pressed steel and the inner friction surface is coated with sintered brass.

Applies to: 2007–2010; MMT6

Transmission, general

MMT6 is a six shift manual transmission. All gears, including back-up, are synchronized. The synchronizing units, interlock ball, springs and sliding block make up a single unit. This design facilitates service work on the synchronizing unit.

The transmission is intended to be part of a transverse drive line with front wheel drive.

The transmission and final drive are constructed together in a common housing made of aluminum. The transmission is very compact. The transmission is a "light weight model" within its class and weighs 52.5 kg (115.7 lbs) without fluid.

The transmission has a maximum torque transfer of 350 Nm.

The transmission fluid is synthetic and does not normally need to be changed. The oil is heat resistant and tolerates high loads. Fluid is topped up via the filler pipe. The fluid is checked via the level plug. The fluid is drained through the drain plug in the base of the transmission.

The gear wheels are located on three shafts.

• One input shaft, the primary shaft
• Two output shafts, the upper and lower secondary shafts.

The transmission housing only has a sealing ring. The seal consists of a liquid gasket.

Transmission, internal components

All driven gear wheels in the transmission are on the input shaft. The input shaft is solid. The input shaft has a ball bearing and a roller bearing. This design solution does not require preloading or adjustment shims. The seal for the input shaft is pressed into the clutch cover.

Transmission input shaft

The gear wheel for 1st and 2nd gears are an integrated part of the input shaft. The gear wheel for 3rd and 5th gears and the gear wheel for 4th and 6th gears are pressed on the shaft.

Due to the extreme pressure used when the gear wheels are pressed on the shaft, they cannot be pressed loose during service work. A defective input shaft can only be replaced as a complete unit.

Defective bearings can be pressed loose and replaced.

The transmission output shaft, gears 1, 2, 3 and 4

The output shaft for 1st, 2nd, 3rd, and 4th gears is hollow. The internal oil ducts lubricate the needle bearings and the roller bearings and the synchronizing units. The output shaft for 1st, 2nd, 3rd, and 4th gears runs on the conical roller bearing. This bearing assembly operates on condition that the shaft is preloaded. Shims are used to achieve this preloading.

The output final drive gear on the output shaft for 1st, 2nd, 3rd and 4th gears is an integrated part of the shaft.

Transmission output shaft, 5th, 6th and back-up gears

The output shaft for 5th, 6th and back-up gears is hollow. The internal oil ducts lubricate the needle bearings and the roller bearings and the synchronizing units.

The output shaft for 5th, 6th and back-up gears runs on conical roller bearings. This bearing assembly operates on condition that the shaft is preloaded. Shims are used to achieve this preloading.

The output final drive gear on the shaft for 5th and 6th and back-up gears is an integrated part of the shaft.

An oil collection ring has been installed on both output shafts.

Gear selector, internal

The shift unit is in the transmission housing and is secured by four screws. The shift unit consists of:

• Aluminum housing with integrated bearing and integrated seal
• Support with integrated selector guide
• Bearing, gear selector gate and end stop for the lateral movement arm.

The shift unit is consolidated in a shift control unit assembly.

Back-up gear in the gear selector assembly is furthest to the left and forward. Neutral is between 3rd and 4th.

The reversing light switch is in the shift control unit and is actuated by the shaft for lateral movement. The reversing light switch is directly connected to the Central Electronic Module (CEM).

The shift control unit must not be taken apart. In the event of a fault, the entire control unit must be replaced.

Four gear selector forks transfer the movement from the selector unit to the relevant coupling sleeve.

Gear selector assembly and mechanical transmission cables

1. Ventilation
2. Adjustment mechanism for mechanical gear selector cables
3. Gear shift lever
4. Mechanical transmission cable for lateral travel
5. Gear selector assembly
6. Gear selector lever and gear knob
7. Ball and lever for mechanical gear selector cables
8. Mechanical gear shift cable
9. Body lead-in (seal in the cowl, made of rubber)
10. Mechanical cable bracket
11. Ball and lever for mechanical gear shift cables
12. Reversing light switch
13. Shift unit.

The movements of the gear selector lever are transferred to the transmission via the two mechanical cables. This requires limited force for gear shifts and ensures that each gear selection is distinct. Vibration and other movement from the transmission is not felt through the gear selector lever.

The mechanical gear shift cables are color marked to reduce the risk of mixing up the cables.

• The end of the mechanical transmission cable for lateral travel is gray
• The end of the mechanical shift cable is black.

The mechanical transmission cable for lateral travel crosses the shift cable in the engine compartment.

Only the mechanical transmission cable for lateral travel can be adjusted. The mechanical transmission cable for lateral travel is adjustable lengthwise. The adjuster is positioned on the mounting towards the lever on the transmission (1). When adjusting, the spring in the gear selector assembly pulls the mechanical cable and then the mechanical cable is locked by hand using the catch. When locking, the gear selector lever must be in the neutral position and the components in the transmission must be in shift position 3 or 4.

The mechanical cables sleeves are secured in the gear selector assembly using quick-release connectors and to cable bracket on the transmission. The mechanical cables ends are secured with ball joints to the gear selector assembly and to the levers in the transmission.

In the event of a faults or damage with any of the mechanical cables, both mechanical cables must be replaced at the same time.

There is a return spring on the lateral movement lever. The shift control unit in the transmission also has a return spring.

Spring-loaded reverse inhibitor (- 2005)

The reverse inhibitor consists of a spring-loaded detent in the gear selector assembly.

Mechanical reverse inhibitor (2006 -)

1. Pin
2. Stop

To prevent the accidental engagement of reverse gear, the gear selector assembly has a mechanical reverse inhibitor. The inhibitor consists of a pin (1) that sits on the gear selector lever and a stop (2) that sits on the gear selector assembly. When the gear selector lever is moved to the left, the pin is pressed against the stop. This prevents the lever from moving farther to the left than the position between 1st and 2nd gear.

To engage reverse, the lever must be pressed down so that the pin goes under the stop.

Differential

1. Conical roller bearing, transmission housing
2. Differential unit
3. Conical roller bearing, clutch housing
4. Bearing shell, conical roller bearing
5. Crown wheel bolts
6. Crown wheel
7. Bearing shell, conical roller bearing

The differential distributes power equally between the drive wheels, even if the drive wheels are rotating at different speeds.

Synchronization

1. Companion flange section
2. Synchronizing hub
3. Coupling sleeve.

The synchronizing units, interlock ball, springs and companion flange section make up a single unit. The synchronizing rings are made of brass. 1st, 2nd, 3rd and 4th gears have double synchronizing rings. 5th, 6th and back-up gears have a single synchronizing ring.

The synchronizing units for 1st, 2nd, 3rd and 4th gears are on the output shaft for 1st, 2nd, 3rd and 4th gears.

The synchronizing units for 5th, 6th gear and back-up gears are on the output shaft for 5th, 6th and back-up gears.

Clutch, general

The clutch is between the engine and transmission. It consists mainly of a pressure plate and a clutch driven plate. The clutch transfers torque to and from the transmission and then on to drive the wheels.

The clutch is a single disc dry clutch. The clutch disc is connected to the transmission input shaft.

On vehicles with more powerful engines, self-adjusting clutches are used to lower the engagement forces.

MMT6 has self-adjusting clutch of the XTend type.

Hydraulic clutch control mechanism

1. Dual mass flywheel
2. Air-bleed nipple
3. Hydraulic hose
4. Master cylinder
5. Clutch slave cylinder
6. Pressure plate (self-adjusting).

Clutch control is based on a well proven system with hydraulic power transmission.

There are ratios built-in to the system to reduce the force required to transfer torque:

• pedal ratio
• hydraulic ratio
• clutch pressure springs ratio.

The force is reduced from approximately 8600 N at the clutch to approximately 100 N at the pedal.

Shock load limiter

If the clutch pedal returns too quickly, the drive line could be damaged by the high torque. There is a shock load limiter in the clutch to avoid this. The shock load limiter chokes the flow between the clutch slave cylinder and the master cylinder if there is a danger of excessive torque. The shock load limiter is in the air bleed adapter on the clutch cable.

Clutch slave cylinder

1. Throwout bearing
2. Protective cap
3. Pressure spring
4. Hydraulic duct
5. Radial seal
6. Plastic housing.

During unaffected conditions the clutch slave cylinder applies a pressure of 100 N on the throwout bearing on the diaphragm spring to the clutch pressure plate. This reduces wear on the throwout bearing. The throwout bearing does not need to accelerate to engine speed when the clutch is engaged.

The hydraulic clutch system is bled via the bleed valve. The bleed valve is in the hydraulic line of the feed and return lines.

The self-adjusting clutch mechanism reduces the operating range of the clutch slave cylinder, which protects the radial seal. The clutch slave cylinder therefore only requires replacement if leakage occurs and if the transmission has been removed. This is because dirt and corrosion can cause damage to the seal after the system has been removed.

To achieve a better seal on the transmission, the radial oil seal for the input shaft is not integrated in the clutch slave cylinder.

Self-adjusting clutch ( XTend)

1. Spring
2. Adjustment ring
3. Wear sensor.

A self-adjusting clutch XTend detects the wear on the clutch plate and adjusts the wear using a adjustment mechanism between the sun spring and the clutch housing. The adjustment mechanism maintains the position of the sun spring and ensures that the pedal effort required remains constant throughout the service life of the vehicle.

The advantages of the self-adjusting clutch are:

• Constant load during the entire service life of the clutch
• Increased service life for the clutch driven plate
• Reduced length of stroke for the throw out bearing.

Pressure plate

1. Pressure springs
2. Pressure plate (housing)
3. Ramp
4. Ramp ring.

The clutch is a single disc dry clutch. Pre-tensioned lifting springs connect the clutch housing and the pressure plate.

As self-adjusting clutches cannot be reset when the clutch driven plate has been replaced, the pressure plate must be replaced.

The pressure plate is the diaphragm spring type. Unlike a traditional type, the pressure plate contains an adjustment ring made of steel or plastic. If there is wear, the adjustment ring moves slightly to maintain the engagement position of the clutch.

The fact that the springs are unable to move backwards has the following advantages:

• increased wear capacity
• the clutch cover can be made shorter because space is not required for rearward movement of the diaphragm spring.

Clutch driven plate

The clutch driven plate transfers engine torque to the transmission input shaft. The plate has a damper to reduce idle rattling. The inside of the plate center is lubricated when the plate is mounted at the factory. This reduces friction between the clutch driven plate and the input shaft, which makes shifting easier.

When replacing the clutch driven plate, the input shaft must be lubricated. See the instructions for replacing the clutch.

It is not possible to replace only the clutch driven plate with these types of clutch. The pressure plate and clutch driven plate must be replaced at the same time.

Dual mass flywheel

The dual mass flywheel reduces noise from the transmission and improves drivability.

The dual mass flywheel helps reduce the load on the crankshaft bearings. It also improves shift quality because the flywheel mass on the clutch driven plate is less.

The component parts of the dual mass flywheel can turn in relation to each other. The amount by which they turn depends on the engine load. On the dual mass flywheel the component parts can turn by up to 60 degrees in both directions. A certain amount of turning can be felt between the component parts if a dual mass flywheel is turned.

Clutch pedal

1. Clutch pedal
2. Clutch pedal support spring
3. Body seal
4. Clutch return spring.

The clutch pedal on vehicles with MMT6 transmissions, has a support spring which reduces the load force on the clutch. The support spring is angled and therefore functions as a pressure spring in a certain clutch pedal position, thus supporting the pedal force.

Applies to: 2007–2013; MTX75

Clutch, general

The main tasks of the clutch system are:

• torque transfer
• disengagement during shifting
• making a comfortable start possible
• be an effective vibration damper to eliminate noise and vibrations in the chassis and drive train.

The clutch is located between the engine and the gearbox. It consists primarily of a pressure plate and a disc. The clutch connects the torque from the engine to and from the gearbox and thereby to driving of the wheels.

The clutch is a single plate dry disc clutch. The disc is connected to the input shaft of the gearbox.

For vehicles with engine D4164T, a self-adjust clutch is used to obtain low clutch forces.

Hydraulic clutch control

1. Dual mass flywheel
2. Bleed nipple
3. Hydraulic hose
4. Master cylinder
5. Control cylinder
6. Pressure plate

The clutch control is based on a system with hydraulic power transmission.

Clutch plate

The clutch plate is the component that transfers the torque to the input shaft and into the gearbox. The clutch plate is also used to produce a gentle, comfortable vehicle start.

The plate has no damping or friction elements. These functions are instead integrated in the dual mass flywheel.

The plate has an adjustable hub that adjusts the centring between the gearbox primary shaft and the engine crankshaft. This is known as a radially travelling hub.

The inside of the plate centre is greased when the plate is fitted at the factory. This reduces the amount of friction between the plate and the input shaft to make shifting easier.

If the plate is replaced, the input shaft should be lubricated. See the instructions for clutch replacement.

Concentric slave cylinder

Clutch control is completely hydraulic, meaning that the slave cylinder sits within the clutch cover. There is no mechanic transfer (fork) in the clutch cover from an external slave cylinder.

The slave cylinder is concentric because it is integrated in the release bearing.

The concentric slave cylinder is highly efficient, centres the release bearing well and is reliable.

The unit is mounted with two screws in the cover of the gearbox. The bearings and sliding surfaces do not require lubrication. The bearing on the concentric slave cylinder is self-centring to the clutch fan.

The hydraulic line from the master cylinder is connected to the concentric slave cylinder via an adapter. The adapter houses a bleed nipple.

To reduce the force required for torque transfer, several reductions are incorporated into the system:

• pedal reduction
• hydraulic reduction
• clutch finger reduction.

Force is reduced from approx. 7800 N force on the clutch to approx. 80 N pedal force.

Shock load limiter

If the clutch pedal returns to its original position too quickly, the high torque could damage the drive train. To avoid such damage, the clutch is equipped with a shock load limiter, which restricts the flow between the concentric slave cylinder and the master cylinder if there is a risk that the torque will become too great. The shock load limiter is housed in the angle adapter beneath the bleed nipple.

Self-adjusting clutch ( XTend) (only D4164T)

1. Spring
2. Adjuster ring
3. Wear detector

The size of the clutch has increased as more powerful engines have been introduced.

A self-adjusting clutch ( XTend) eliminates problems with both wear capacity on the pressure plate and clutch plate and the increase in pedal force when the lining is worn. The self-adjusting clutch eliminates the increased load caused by increased wear. The advantages of a self-adjusting clutch are as follows:

• Constant load throughout the entire service life of the clutch.
• Increased service life of the clutch plate.
• Reduced stroke for the release bearing.

A self-adjusting clutch XTend detects the wear on the clutch plate and adjusts the wear using a adjustment mechanism between the sun spring and the clutch housing. The adjustment mechanism maintains the position of the sun spring and ensures that the pedal effort required remains constant throughout the service life of the vehicle.

Pressure plate (D4164T only)

1. Compression springs
2. Pressure plate (housing)
3. Ramp
4. Ramp ring

The clutch is a single plate dry disc clutch. Pretensioned lifting springs connect the clutch housing and the pressure plate.

Because self-adjusting clutches cannot be reset when the clutch plate has been replaced, the pressure plate must also be replaced.

The pressure plate is fan-shaped. This differs from a traditional type in that the pressure plate contains an adjuster ring that is made of plastic or steel. When wear begins to show, the adjuster ring is automatically moved slightly so that the work mode of the clutch remains constant.

The following advantages stem from the compression springs not moving rearward:

• the wear capacity can be increased
• the clutch cover can be made shorter since space is not needed for the fan to move rearward.

Dual mass flywheel (DMF)

The dual mass flywheel reduces noise from the gearbox and improves driveability.

The dual mass flywheel also contributes to reducing the load on the engine crankshaft bearing and improving shift quality since the flywheel mass of the clutch plate is less.

The components of the dual mass flywheel can rotate in relation to one another. This twisting depends on the load from the engine. Twisting of the dual mass flywheel is up to 60 degrees in both directions. You can feel a certain twisting between the components if you turn a dual mass flywheel.

Gearbox, general

1. Clutch cover
2. Input shaft
3. Differential
4. Output shaft
5. Reverse idler gear
6. Gearcase
7. Outer shift mechanism

MTX-75 is a five-speed manual gearbox. The gearbox and differential are integrated in the same housing. The two cast aluminium housing halves are called the gearcase and clutch cover. A floating seal sits between the two housing halves. The gearcase has been equipped with an extra reinforcement rib, which reduces noise and vibrations.

The gearbox has two parallel shafts. All gearwheels are in constant mesh. The different gear ratios are obtained with a gearwheel pair for each gear.

When reverse gear is engaged, an idler gear reverses the output shaft's direction of rotation.

The output shaft is in constant mesh with the final drive.

All impellers, including the reverse gearwheel, have bevelled cogs and are mounted on needle bearings.

In neutral, no impellers are connected to the input or output shaft via the synchromesh unit. No torque is transferred to the differential.

The input and output shaft are mounted in the gearbox, each with a roller bearing in the clutch cover (1) and a roller bearing in the gearcase (6).

The final drive rack is in constant mesh with the crown wheel of the differential.

Gear lever movements are transferred to the gearbox via two thick cables. This generates low shift forces and distinct positions.

All gears are synchronised. 1st and 2nd gears have double synchronisation. 3rd, 4th, 5th and reverse gears have single synchronisation.

The gearbox oil is synthetic and normally does not require changing. The oil is heat resistant and can handle high loads. The oil level is checked and topped up via the level plug. Oil is drained through the drain plug at the bottom of the gearbox. For more information on oil and capacity, see Specifications, Gearbox.

Inner gearbox components

All impellers and gearwheels have bevelled cogs, which make the cogs extend over a longer distance without changing the width between the impeller and gearwheel. This results in better contact between the wheels, which leads to higher forces being transmitted. The noise level is also lower.

Reverse gear also has bevelled cogs and thus works as quietly as other gear in the gearbox.

The ring gear with final drive rack is found in the differential housing, which contains a differential gear (with and without drive shaft splines) and planetary gear with lock.

Input shaft, primary shaft

The input shaft is mounted on conical roller bearings - one in each cover.

The 3rd and 4th gear impellers sit on the input shaft.

Shift fork for 3rd and 4th gears

The input shaft is positioned above the output shaft in the gearbox. To provide lubrication to 3rd and 4th gear synchromesh units, the shift forks are equipped with a guide plate which provides oil to the synchromesh units.

Output shaft, secondary shaft

The output shaft is mounted on conical roller bearings - one in each cover.

The 1st, 2nd, 5th and reverse gear impellers sit on the output shaft.

The final drive rack is an integrated component of the output shaft.

Reverse idler gear

1. Reverse shaft mounting
2. Thrust washer
3. Reverse idler gear (small collar down)
4. Needle bearing
5. Thrust washer

The reverse idler gear is driven by the input shaft. Its function is to change the output shaft's direction of rotation when reverse gear is engaged. The reverse idler gear runs on a needle bearing on the idler gear shaft.

Shifter

The gearbox has four shifting rods, three of which house shift forks.

The shifting motion is transferred from the gear lever to the gearbox via double cables.

The torsion pin mounted on the shaft for shift travel executes the longitudinal shift movement. The shift fork and gate are located on the input shifting rod, which is connected to the lever for lateral travel.

The lateral travel cable can be adjusted, but the longitudinal cable cannot. If either wire has a fault or is damaged, both cables must be replaced together.

The inner shifter in the gearbox is mounted in bearings lubricated with gearbox oil.

Reverse detent

A spring-loaded reverse detent, which is located in connection to the gear selector gate, prevents the gear lever from being unintentionally shifted from the 5th gear position to reverse. The reverse detent usually rests in a recess on the gear selector gate.

Differential

The main components of the differential are:

• ring gear
• differential shaft
• four conical gearwheels positioned at right angles to one another
• differential housing with two roller bearings.

The gearbox and differential are mounted in a two-component aluminium housing that is mounted on the engine with a flange.

The drive shafts have splines and are locked with a lock ring.

The differential is pretensioned via shims that sit between the gearcase and the conical roller bearing.

Synchronisation

The synchroniser hub assembly consists of a coupling sleeve, drive piece and synchroniser hub. Each synchroniser hub is connected to its shaft via splines and rotates with it.

An impeller that can rotate freely on the shaft sits on each side of each synchroniser hub. Each impeller is in constant mesh with its respective gearwheel. The synchronisation kit is located between the synchroniser hub and the impeller.

The synchromesh units have the following positions on the shafts in the gearbox:

• The 1st, 2nd, 5th and reverse gear synchromesh units sit on the output shaft
• The 3rd and 4th gear sychromesh unit sits on the input shaft.

The following have single synchronisation:

• reverse gear
• 3rd gear
• 4th gear
• 5th gear.

The following have double synchronisation:

• 1st gear
• 2nd gear.

Applies to: AW55-50/51SN

Transmission, general

The automatic transmission has five forward gears and one back-up (reverse) gear. The fifth gear is an overdrive which saves fuel during highway driving.

The mechanical components of the transmission are enclosed within the torque converter cover, the transmission housing and valve housing.

Gearshifts are controlled by an hydraulic operating system. Gearshifts take place without freewheeling and completely automatically in terms of load and speed.

The solenoid valves are located under the valve housing cover on the transmission, in the valve housing for the hydraulic system. These are activated by the transmission control module (TCM).

The transmission input speed sensor is electro-magnetic and acts on a toothed pulse wheel. By comparing the engine and transmission speeds, the control module can determine the amount of slippage in the torque converter.

The gear-shift position sensor has three separate functions:

• using an electrical route to inform the transmission control module (TCM) of the selected gear position
• to activate the back-up (reverse) light when the gear selector is in R-position
• To allow engine start if the gear selector is in P or N-position. This signal is also transmitted to the engine's control system and is used for drive position compensation of idle.

The transmission and final drive share a common oil pan. A dipstick in the transmission is used to check the oil level in the transmission.

Torque converter

The torque converter is between the engine and the automatic transmission.

When the engine is idling the pump effect is too weak to drive the turbine and the vehicle will not move. As the engine speed (RPM) rises it successively starts to drive in a gradual way. At higher engine speeds (RPM) the power transfer to the turbine can be up to 95%. The torque converter functions as an hydraulic clutch. It also amplifies the torque of the engine at lower engine speeds and therefore an automatic transmission does not require as many gears as a manual transmission.

The torque converter consists of a round metal casing which contains two impeller wheels and is filled with oil. One of the impeller wheels, the pump wheel, is fixed to the casing. Both are connected to the engine crankshaft and rotate with it. The other impeller wheel, the turbine wheel, is connected to the input shaft of the transmission and is driven by the oil which is pumped around by the pump wheel. The rotating impeller wheels and the oil in the torque converter "slip" slightly and creates a slight loss of power, which raises fuel consumption slightly.

Thanks to a third, smaller wheel, the stator wheel, the torque converter also reinforces the engine torque at low engine speeds.

Differential

The differential distributes power equally between the drive wheels, even if they are rotating at different speeds.

The differential consists of the differential housing, large and small side gears, shaft journals and thrust washers.

The differential has 6 gearwheels. The differential housing is completely sealed so that if a drive shaft is removed no dirt can penetrate and no oil can run out.

Applies to: M66

Transmission general

M66 is a six gear manual transmission. All gears, including back-up (reverse), are synchronized. The transmission is intended to be part of a transverse drive line with front wheel or four wheel drive.

The transmission is built together with the final driven in a common aluminum housing. This unique construction makes the transmission very compact while enabling it to transmit high torque.

The engine and transmission have damped mountings, either on the side members with pendulum mounting or on a sub frame.

The transmission and final drive are extremely compact. For further information about dimensions, see Specifications, transmission.

The oil is synthetic and does not normally need to be changed. The oil is heat resistant and tolerates high loads. The hole in the level plug is used to top up the oil and check its level. The oil is drained through the drain plug in the base of the transmission.

The gear wheels are located on four shafts. They are:

• input shaft (A)
• intermediate shaft 1-2, 5-6 (B)
• intermediate shaft 3-4 (C)
• back-up (reverse) shaft (D).

The clutch gears are welded directly to the idler wheel to shorten the length of the shaft. To further shorten the length of the transmission, needle bearing with inner rings are used instead of snap rings.

The inner rings sit on the shaft inside the idler gears and extend lengthwise a little outside each idler gear. When the components on the shafts are pulled together the inner rings counterhold, so that the idler wheels have the clearance that they require to rotate.

The components of the input shafts are pulled together with a bolt located in the end of the shaft. Components of intermediate shaft 3-4 are held together with a press joint and a bolt located in the end of the shaft. The components of intermediate shaft 1-2, 5-6 are held together with the press joint of the 5th and 6th gear pinion.

Transmission, internal components

Gear selector, internal

The gear selector is in a single complete unit with the exception of the ball limiter for the gear position. This is threaded in the transmission housing. The gear selector is held in position by 4 screws. 2 guide pins in the control housing and a needle bearing in the bottom of the gear selector unit control the position in the transmission housing.

Back-up (reverse) gear in the gear selector assembly is furthest to the right and down. Neutral is between 3rd and 4th.

The back-up (reversing) lamp switch is in the control housing and is affected by the shaft for lateral movement. The back-up (reversing) lamp switch is directly connected to the central electronic module (CEM).

The gear selector unit must not be dismantled. In the event of a fault the whole gear selector unit must be replaced.

4 gear selector forks transfer the movement from the control to the relevant coupling sleeve.

Gear selector assembly and mechanical transmission cables

1. Locking the adjustable mechanical transmission cable for lateral travel
2. Solenoid
3. Gear selector assembly
4. Mechanical cables
5. Mechanical cables bracket.

The mechanical cables are in a cable assembly. In the event of a fault or damage with any of these the whole mechanical cable assembly must be replaced.

The cable sleeves are secured using quick connectors in the gearshift assembly and in the cable bracket on the transmission.

The mechanical transmission cable for lateral travel is adjustable lengthwise. The adjuster is positioned on the mounting towards the lever on the transmission (1).

The gear selector assembly is made of plastic. It has rubber feet (to reduce noise and vibration).

The gear selector assembly has a lever and a lever arm. There is a return spring on the lateral movement lever.

Back-up (reverse) inhibitor

The shift lever assembly houses a solenoid that serves as an electronically controlled reverse inhibitor.

There is an electronic damping function on the solenoid which gives the solenoid a soft action. This reduces noise. The solenoid can be replaced.

Differential

The differential distributes drive shaft torque equally between the drive wheels, even if they are rotating at different speeds.

The differential consists of the differential housing, large and small side gears, shaft journals and thrust washers.

Applies to AWD

On the M66 AWD a sleeve for power transfer is located on the differential.

Synchronization

The synchronizing hub assembly consists of a coupling sleeve, flange and the hub. Each synchronizing hub is joined to its shaft by splines and rotates with it.

There are idler wheels on both sides of each synchronizing hub. The idler wheels rotate freely on the shaft (does not apply to reverse gear). Each idler wheel is constantly engaged in its pinion. The synchronizing set is positioned between the synchronizing hub and the idler wheel.

The synchronizing units are positioned on the shafts in the transmission as follows:

• The synchronizing unit for 1st - 2nd gear is on the intermediate shaft 1-2, 5-6
• The synchronizing unit for 3rd - 4th gear is on the intermediate shaft 3-4
• 5th-6th the synchronizing unit is on the input shaft
• the synchronizing unit for back-up (reverse) gear is on the back-up (reverse) shaft.

The synchronizing rings expand when heated by the same amount as the components they are in contact with. As a result no safety margin is required to counter expansion.

The idler wheels for single and double synchronization have no cones. An inner ring on the synchronizer unit performs this function instead.

The synchronizer unit is a modular system. This makes it easy to upgrade from a single synchronizer to double synchronization by replacing the synchronizer kit.

Single synchronization, which has one friction surface, is on:

• back-up (reverse) gear
• 4th gear
• 5th gear
• 6th gear.

The outer ring (to the left in the illustration) is manufactured in pressed steel. The inner ring is pressed steel and the friction surface is coated with sintered brass.

Double synchronization, two friction surfaces, is on:

• 3rd gear.

The outer ring (to the left in the illustration) is manufactured in pressed steel. The sealing ring is pressed steel and the friction surfaces are coated with sintered brass. The inner ring is machined steel.

Triple synchronization, three friction surfaces, is on:

• 1st gear
• 2nd gear.

The outer ring (left in the illustration) is made of pressed metal. The intermediate ring is made of pressed metal with a sintered brass coating on the friction surfaces. The inner ring is of pressed metal with a sintered brass coating on the inner friction surface. Triple synchronization also includes a ring integrated with the idler wheel.

Clutch, general

The main task of the clutch system is to transfer torque, disengage during shifting, allow comfortable starting and to act as an efficient vibration damper to eliminate noise and vibration in the chassis and drive train.

The clutch is located between the engine and the transmission. The main components are a pressure plate and a clutch driven plate. The clutch is used to connect the torque from the engine to and from the transmission and therefore to drive the wheels.

The clutch is a single disc dry clutch. The clutch disc is connected to the transmission input shaft on the transmission.

On vehicles with more powerful engines, self-adjusting clutches are used to lower the engagement forces.

Hydraulic clutch control mechanism with concentric slave cylinder (CSC)

The clutch control mechanism is fully hydraulic. The slave cylinder is inside the clutch cover. There is no mechanical transfer (fork) inside the clutch cover from an external slave cylinder.

The concentric slave cylinder (CSC) means that the slave cylinder is integrated with the throwout bearing.

The concentric slave cylinder (CSC) is extremely efficient and reliable and the throwout bearing is accurately centered.

The unit is mounted with a bolt in the gearcase. The bearings and sliding surfaces do not require lubrication. The bearing on the concentric slave cylinder is self-centering to the clutch fan.

The hydraulic line from the master cylinder is connected to the concentric slave cylinder (CSC) via an adapter. There is a bleed nipple on the adapter.

There are ratios built-in to the system to reduce the force required to transfer torque:

• pedal effort
• hydraulic force
• clutch finger force.

The force is reduced from approximately 8600 N at the clutch to approximately 100 N at the pedal.

If the clutch pedal returns too quickly, the drive line could be damaged by the high torque. There is a shock load limiter in the clutch to avoid this. The shock load limiter chokes the flow between the concentric slave cylinder (CSC) and the master cylinder if there is a danger of the excessive torque. The shock load limiter is in the concentric slave cylinder.

Shock load limiter

In vehicles with engines with high engine torque the return time of the clutch pedal may be too short. This means that the torque peak is so high that it can damage the driveline.

In the event of the torque peak being to high, the hydraulic flow in the engagement direction is choked between the concentric slave cylinder (CSC) and the master cylinder using a shock load limiter.

Self-adjusting clutch (SAC)

A self-adjusting clutch (SAC) eliminates problems both in terms of wear in the clutch cover and the need for increased force at the pedal as the facing thickness reduces.

This considerably increases the life of the clutch. A self adjusting clutch will not normally require replacement during the lifetime of the vehicle.

A self-adjusting clutch (SAC) senses the increase in release load at the diaphragm spring. It has a adjustment mechanism between the diaphragm spring and the clutch housing. This maintains the position of the diaphragm spring and ensures that the pedal effort required remains constant throughout the service life of the vehicle.

The pressure plate is of the diaphragm spring type. Unlike a traditional type, the pressure plate contains an adjustment ring made of steel or plastic. If there is wear, the adjustment ring moves slightly to maintain the engagement position of the clutch.

The fact that the fingers are unable to move backwards has the following advantages:

• increased wear capacity
• the clutch cover can be made shorter because space is not required for rearward movement of the diaphragm spring.

Clutch driven plate

The clutch driven plate is the component that transfers the torque to the input shaft and into the transmission.

The clutch driven plates of today do not have dampers or friction elements. These functions are integrated in the dual mass flywheel.

The clutch driven plate center is greased internally when the clutch driven plate is installed at the factory. This reduces the friction between the clutch driven plate and the input shaft to make shifting easier.

When replacing the clutch driven plate, the input shaft must be lubricated. See the instructions for replacing the clutch.

Dual mass flywheel

The dual mass flywheel reduces noise from the transmission and improves drivability.

The dual mass flywheel helps reduce the load on the crankshaft bearings. It also improves shift quality because the flywheel mass on the clutch driven plate is lower.

The components of the dual mass flywheel can rotate in relation to one another. This twisting depends on the load from the engine. Twisting of a dual mass flywheel is up to 60 degrees in both directions. You can feel a certain twisting between the components if you turn a dual mass flywheel.